The present invention relates to a fluorescent discharge tube and a bulb-shaped fluorescent lamp using the same.
Conventionally, three types of fluorescent lamps, for example, bulb-shaped fluorescent lamps, with luminous fluxes corresponding to 40 W, 60 W, and 100 W general electric lights have been developed and commercially expanded. Among these three types, the development of the fluorescent lamps with luminous fluxes corresponding to 60 W and 100 W general electric lights, which have high sales distribution ratios, has been continued. Recently, particularly in order to replace small general electric lights, the size of lamps is reduced increasingly in lamp design. Bulb-shaped fluorescent lamps having discharge tubes with various configurations have been proposed and commercialized.
As shown in FIGS. 11 and 12, a discharge tube formed of three U-shaped glass tubes joined with bridge junctions has been used in conventional bulb-shaped fluorescent lamps. In such a discharge tube, high lamp efficiency is achieved by increasing the length of a discharge path, and the size reduction of the lamp as an object also is achieved (JP 1-220360 A and JP 9-147795 A). Similarly, as shown in FIG. 13, a discharge tube formed of four U-shaped glass tubes joined together to increase the length of a discharge path also has been known (JP 9-106782 A).
However, in a bulb-shaped fluorescent lamp using a discharge tube formed of at least three U-shaped glass tubes having a long discharge path and many bends, an inherent problem arises because the lamp requires a longer rise time with respect to luminous flux at a start of its operation than that in, for example, a conventional discharge tube formed of two U-shaped glass tubes joined together.
Therefore, in order to improve such characteristics in rise time with respect to luminous flux (hereinafter referred to as xe2x80x9cluminous-flux rise characteristicsxe2x80x9d), a layout method in which one main amalgam 55 and four auxiliary amalgams 52, 53, 56, and 57 are combined, as shown in FIG. 11, is disclosed. That is, one main amalgam 55 is placed inside a small tube 54 at an end of a U-shaped glass tube positioned at an end of a discharge tube 46. On the other hand, the two auxiliary amalgams 52 and 53 are placed in locations adjacent to electrodes 50 and 51, respectively, and the other additional auxiliary amalgams 56 and 57 are placed at both end portions of the U-shaped glass tube 48 and in a discharge path.
As shown in FIG. 12, in a discharge tube 58 formed of three U-shaped glass tubes 59, 60, and 61, a layout method in which two main amalgams 66 and 67 and three auxiliary amalgams 68, 69, and 70 are combined is employed. That is, the two respective main amalgams 66 and 67 are placed inside small tubes 64 and 65 at one end of the U-shaped glass tubes 59 and 61, respectively, positioned at the ends of the discharge tube 58. On the other hand, the two auxiliary amalgams 68 and 69 are placed in locations adjacent to electrodes 62 and 63, respectively, and another additional auxiliary amalgam 70 is positioned at an end portion of the U-shaped glass tube 60 and in a discharge path.
Furthermore, as shown in FIG. 13, in a discharge tube 75 formed of four U-shaped glass tubes 71, 72, 73, and 74, a layout method in which one main amalgam 81 and three auxiliary amalgams 78, 80, and 79 are combined is employed. That is, the two auxiliary amalgams 78 and 79 are provided in the vicinities of the electrodes 76 and 77 at the ends of the discharge tube 75. The other auxiliary amalgam 80 is provided at an end portion of the U-shaped glass tube 72 so as to be positioned substantially midway in a discharge path. The main amalgam 81 is placed at a location adjacent to the auxiliary amalgam 80 at an end of the U-shaped glass tube 73.
Such conventional techniques can achieve the size reduction in bulb-shaped fluorescent lamps using discharge tubes formed of at least three U-shaped glass tubes joined together, but still cannot obtain sufficient luminous-flux rise characteristics. In other words, while general electric lights have a luminous flux value corresponding to 100% of the luminous flux during a stable operation directly after a start of operation, the bulb-shaped fluorescent lamps according to the above-mentioned conventional techniques merely has a luminous flux value corresponding to 20% or lower of the luminous flux during a stable operation, even after three seconds from a start of operation. In this case, according to the study of the present inventors, it was found that the luminous-flux rise characteristics of the lamps depended on the non-operation time after a stop of operation, and particularly, in the case of a relatively short non-operation time of one to six hours after a stop of operation, the lamps required a longer rise time with respect to luminous flux, which was the biggest problem.
Such slow luminous-flux rise characteristics were not a big problem when the lamps were operated continuously for many hours for business use in shops, department stores, and the like in a conventional main application field. However, this problem should be solved when the lamps are to be used for residential lighting which will be turned on and off frequently. It can be said that this problem is a hindrance to the wide use of bulb-shaped fluorescent lamps as lamps for residential lighting.
The present invention is intended to obtain a small fluorescent discharge tube having further improved luminous-flux rise characteristics, even when a non-operation time after a stop of operation is relatively short, and a bulb-shaped fluorescent lamp using the same.
In order to achieve the aforementioned object, a fluorescent discharge tube of the present invention includes at least three U-shaped glass tubes joined to form one body, electrodes provided at the ends thereof, and one discharge path formed therein. In the vicinities of the electrodes, first auxiliary amalgams are provided, and main amalgams are positioned at least in two locations in the discharge path between the electrodes. At least in one location, a second auxiliary amalgam is positioned between the main amalgams.
A bulb-shaped fluorescent lamp of the present invention includes a fluorescent discharge tube and a lighting circuit. The fluorescent discharge tube includes at least three U-shaped glass tubes joined to form one body, electrodes provided at the ends thereof, and one discharge path formed therein. In the vicinities of the electrodes, first auxiliary amalgams are provided, and main amalgams are positioned at least in two locations in the discharge path between the electrodes. At least in one location, a second auxiliary amalgam is positioned between the main amalgams.